One common method of fixing fractured bones is to use a plate and screws to secure the bone fragments. In this method, screws are inserted through holes in the plate in order to secure the fragments to the plate. Although this technique is effective when the fragments are relatively large in relation to the diameter of the screw, when the fragment size is small in relation to the diameter of the screw, the size of the screw hole required in the bone fragment can weaken the fragment and cause it to fragment further, resulting in failure of fixation. Additionally, standard bone screws require thread purchase in the bone in order to compress the fragment against the undersurface of the plate in order to provide stability. If the fragments are small or consist of poor quality bone, thread purchase can be inadequate, resulting in failure of fixation.
In my previous U.S. patents (U.S. Pat. Nos. 5,931,839 and 7,044,951 plates have been disclosed that utilize small pins that are placed through the plate and into the bone fragments. This alternative type of fixation reduces the risk of causing additional fragmentation of a small fragment by reducing the hole size needed for fixation. In addition, since the pin does not depend on thread purchase in the bone fragment, this technique avoids the failure caused by poor purchase of screw threads.
Although the pin plates provide these advantages, the fixation by the pin is biomechanically different from that provided by a screw in a plate. In U.S. Pat. No. 5,931,839, the pin is not secured to the plate, but only restricts translational movement of the pin in relation to the surface of the plate. In this type of implant, axial movement of the pin in the hole as well as angulation of the pin within the hole are not constrained. If the pin is not rigidly secured into an opposite stable bone fragment, this may result in failure of fixation.
In U.S. Pat. No. 7,044,951 the pin is stabilized to the plate by modifications in the plate. Some of the modifications of the plate (FIGS. 3, 3A, 5, 6, 6A, 7, 8, 9, 10, 11, 12, 13, 14, 24, 25, 26) are constructed to provide a channel or aperture that prevents the pin from backing out of the bone. These embodiments limit axial movement of the pin but do not constrain angular movement of the pin. In other modifications (FIGS. 15, 16A, 16, 17, 18, 19, 20, 32, 33, 34, 35) the pin is captured by tabs on either side. These types of designs also limit axial movement of the pin out of the pin hole but do not limit angular movement of the pin in relation to the plate. In addition, they are cumbersome to manufacture and complicate the surgery by requiring the surgeon to bend and/or thread the end of the pin through the tabs in the plate. In still other modifications (21, 22, 23, 27, 28, 29, 31, 32, 33, 34, 25) the pin is constrained by frictional purchase of the plate against the side wall of the pin. Like the other embodiments, these modifications limit axial movement of the pin in relation to the plate, but provide less constraint to angular movement. In addition, most of these require the surgeon to crimp a portion of the plate with a bending instrument, which adds to the complexity of the procedure and may be difficult to do because of difficult access to the plate from a limited exposure. In addition, many of these embodiments require the pin to be bent or cut after the pin is in place which adds further to the complexity of the surgery. Finally, since many of these designs leave the end of the pin extending out of the plate, the cut end can cause irritation of the soft tissues and even tendon rupture.